The invention relates to a steel material for producing engine piston upper parts.
In diesel motors, extremely high compressions with good fuel utilization, low emissions and high km life expectancy can be obtained with steel forged piston upper parts. In this connection, the piston upper parts are generally quenched and tempered from the material 42CrMo4 in a range from 800 to 1100 N/mm.sup.2, i.e. hardened by heating from room temperature to 860.degree. C. and subsequently quenching in heavy-duty oil and tempered by renewed heating to ca. 480.degree. to 660.degree. C. with final cooling in a container. The temperatures in the hardening and/or tempering furnace are adjusted according to the respective steel analysis and the customer instructions with respect to strength.
The wear, corrosion and thermal resistance properties of the piston upper parts which are required by the consumer can only be obtained with the above mentioned steel and the forging method. However, the construction principle of the pendulum shaft piston with a steel forged upper part and aluminum skirt has the disadvantage that the motor is expensive in comparison to the one-piece pistons produced from aluminum which is also caused by the quenching and tempering (heat treatment) of the steel piston upper part.
The object of the present invention is to provide a material with which steel forged piston upper parts can be produced without quenching and tempering, and hence more economically, without negatively influencing the wear, corrosion and heat resistance properties.